export and import are backwards compatible. What that means is that IMP can read and use a file from an earlier release of EXP -- but it cannot in general read and use a file from a LATER release of EXP.

So, if the export of the 8.0.6 database was done via the 8.0.6 export tool -- in general, it will NOT be the case that the 8.0.5 import tool can read it. I know for a fact that if you export from 8.1.6, 8.1.5 cannot read the dmp file at all (file format changed between releases). Another issue is that there will be objects in the new release that simply did not exists in the earlier versions and that will break the import.

You should use the 8.0.5 export tool over Net8 to the 8.0.6 database to create the export file. Then, both 8.0.5 and 8.0.6 will be able to use it. Note however that if there are any features/functions of 8.0.6 that are not available in 8.0.5 -- the 8.0.5 export tool will not export it.